OFDM channel estimation system and method components

Abstract

Channel estimation for high mobility OFDM channels is achieved by identifying a set of channel path delays from an OFDM symbol stream including carrier data, inter-channel interference noise and channel noise; determining the average channel impulse response for the identified set of channel path delays in each symbol; generating a path delay curvature for each channel path delay in each symbol based on stored average channel impulse responses for the identified channel path delays; estimating the carrier data in the symbols in the OFDM symbol stream in the presence of inter-channel interference noise and channel noise from the OFDM symbol steam and the average impulse responses for the identified channel path delays; reconstructing the inter-channel interference noise in response to the path delay curvature, the identified set of channel path delays and estimated carrier data to produce a symbol stream of carrier data and channel noise with suppressed inter-channel interference noise.

What is claimed is: 
     
       1. A system comprising:
 an average channel estimator circuit, responsive to an Orthogonal Frequency Division Multiplexing (OFDM) symbol stream and a set of channel path delays, comprising: 
 an extraction circuit for extracting an OFDM symbol from the OFDM symbol stream; 
 an input circuit for receiving a set of channel path delays corresponding to the OFDM symbol, each path delay corresponding to one of a plurality of transmission paths between a transmitter and a receiver; and 
 an estimator circuit for estimating, for each of the plurality of transmission paths, an average path gain corresponding to each of the set of channel path delays based on least squares and known noise; 
 a curve generator circuit communicatively coupled to the average channel estimator circuit, and responsive to stored average impulse responses, comprising:
 a selection circuit for selecting, from storage, average channel gains of neighboring OFDM symbols; 
 a rate determining circuit for determining a rate of change of the neighboring average channel gains; and 
 a model selection circuit for identifying a best-fit average free curve for the stored channel impulse responses, 
 wherein the model selection circuit selects an order of the best-fit average free curve based on the determined rate of change and wherein an average of the best-fit average free curve comprises an average channel response; and 
 
 a carrier data estimator circuit communicatively coupled to the average channel estimator circuit, responsive to the OFDM symbol stream and average impulse responses from the average channel estimator circuit, for estimating the carrier data in the symbols in the OFDM symbol stream in the presence of inter-channel interference and channel noise, comprising:
 a vector generating circuit for creating a vector with zeroes and inserting average path gains in associated delay locations; and 
 
 an equalization circuit for calculating equalization coefficients. 
 
     
     
       2. The system of  claim 1 , wherein the average channel estimator circuit further comprises a normalizing circuit for extracting a channel frequency response for each of the set of channel path delays using known carriers. 
     
     
       3. The system of  claim 1 , wherein the average channel estimator circuit further comprises a Fourier transform circuit for performing an Fourier transform on the extracted OFDM symbol. 
     
     
       4. The system of  claim 1 , wherein the estimator circuit is configured to perform a fast Fourier transform on the OFDM symbol after it has been extracted by the extraction circuit. 
     
     
       5. The system of  claim 4 , wherein the estimator circuit is configured to normalize the result of the fast Fourier transform. 
     
     
       6. The system of  claim 5 , wherein the result of the fast Fourier transform is normalized according to known carriers. 
     
     
       7. The system of  claim 1 , wherein the carrier data estimator circuit further includes Fourier transform circuit for performing a Fourier transform on said vector. 
     
     
       8. The system of  claim 1 , wherein the carrier data estimator circuit further includes an averaging circuit for calculating noise level. 
     
     
       9. The system of  claim 1 , wherein the carrier data estimator circuit further includes a slicer circuit for matching the equalized symbols to a predefined grid of levels. 
     
     
       10. The system of  claim 1 , wherein the selection circuit selects at least two neighboring OFDM symbols. 
     
     
       11. The system of  claim 1 , wherein the rate determining circuit comprises an fast Fourier transform circuit. 
     
     
       12. The system of  claim 1 , wherein the best-fit average free curve comprises a first order curve. 
     
     
       13. The system of  claim 1 , wherein the best-fit average free curve comprises a higher order curve. 
     
     
       14. The system of  claim 1 , wherein the order of the best-fit average free curve is selected from the group comprising a first-order curve and a higher-order curve. 
     
     
       15. The system of  claim 1 , wherein the order of the best-fit average free curve is selected from the group comprising a best-fit straight line and a parabolic shape. 
     
     
       16. A method Orthogonal Frequency Division Multiplexing (OFDM) channel estimation comprising:
 estimating an average gain for each of a plurality of paths in a channel, comprising:
 extracting an OFDM symbol from an incoming OFDM symbol stream; 
 receiving a set of channel path delays corresponding to the OFDM symbol, each path delay corresponding to one of a plurality of transmission paths between a transmitter and a receiver; 
 performing, using a digital-signal processor, a fast Fourier transform on the extracted OFDM symbol; 
 normalizing the results of the Fourier transform by using known carriers to obtain a frequency response of the channel; and 
 estimating an average path gain for each of the plurality of paths in the channel based at least in part on a least-squares model, the channel path delays, and known noise 
 
 generating a path delay curvature for each channel path delay in each symbol in the OFDM symbol stream based on stored average channel impulse responses for the identified channel path delays comprising:
 averaging channel gains of neighboring OFDM symbols; 
 determining a rate of change of the neighboring average channel gains; and 
 identifying a best-fit average free curve for the stored channel impulse responses; 
 wherein an order of the best-fit average free curve is selected based on the determined rate of change and wherein an average of the best-fit average free curve comprises an average channel response; and 
 
 estimating average impulse responses for the identified channel path delays comprising:
 creating a vector with zeros and inserting average path gains in associated delay locations; and 
 calculating equalization coefficients in response to the Fourier transform. 
 
 
     
     
       17. The method of  claim 16 , wherein the best-fit average free curve comprises a first order curve. 
     
     
       18. The method of  claim 16 , wherein the best-fit average free curve comprises a higher order curve. 
     
     
       19. The method of  claim 16 , wherein the order of the best-fit average free curve is selected from the group comprising a first-order curve and a higher-order curve. 
     
     
       20. The method of  claim 16 , wherein the order of the best-fit average free curve is selected from the group comprising a best-fit straight line and a parabolic shape. 
     
     
       21. A computing system comprising:
 a transceiver; 
 a processor configured to receive signals from the transceiver; and 
 a memory having stored thereon logic operable for: 
 estimating an average gain for each of a plurality of paths in a channel comprising:
 extracting an OFDM symbol from an incoming OFDM symbol stream; 
 receiving a set of channel path delays corresponding to the OFDM symbol, each path delay corresponding to one of a plurality of transmission paths between a transmitter and a receiver; 
 performing, using a digital-signal processor, a fast Fourier transform on the extracted OFDM symbol; 
 normalizing the results of the Fourier transform by using known carriers to obtain a frequency response of the channel; and 
 estimating an average path gain for each of the plurality of paths in the channel based at least in part on a least-squares model, the a given set of channel path delays, and known noise 
 
 generating a path delay curvature for each channel path delay in each symbol in the OFDM symbol stream based on stored average channel impulse responses for the identified channel path delays comprising:
 averaging channel gains of neighboring OFDM symbols; 
 determining a rate of change of the neighboring average channel gains; and 
 identifying a best-fit average free curve for the stored channel impulse responses; 
 wherein an order of the best-fit average free curve is selected based on the determined rate of change and wherein an average of the best-fit average free curve comprises an average channel response; and 
 
 estimating average impulse responses for the identified channel path delays comprising:
 creating a vector with zeros and inserting average path gains in associated delay locations; and 
 calculating equalization coefficients in response to the Fourier transform.